The scene in the chintzy Club Ai in Tokyo is a familiar one. A "host" bar in the Kabukicho district of the city, smartly dressed men and women chat to each other over absurdly expensive drinks.

There is laughter and flirting, and more than a hint of sexual tension.

But Club Ai is unusual in one important respect: the customers here are women.

While the host bar industry has long catered for Japanese men in search of young, attractive partners, there is now a burgeoning industry catering for women too, a sign of an important cultural shift.

Club Ai is one of some 100 host clubs and bars for women determined to claim part of Japan's lucrative escort business for themselves.

For some that can mean indulging in as much hard drinking, X-rated conversation and casual sex as men do.

For most, though, a visit to a host club is an escape from the drudgery of work and enforced passivity in what is still a largely patriarchal society. The women who frequent host clubs defy the stereotype of bored, wealthy housewives.

Mutsuko, a boutique owner and regular at Club Ai, is well-dressed, confident and witty. She is typical of the older women who visit before midnight, after which it quickly fills with off-duty hostesses, cabaret club workers and prostitutes who sing, dance and drink until dawn.

"I forget everything when I come here. It's impossible not to when I'm surrounded by so many gorgeous men," she says, as her host for the evening dutifully mixes her drink.

Banter and drinking doesn't come cheap at an upmarket club like this. First-time customers can sit and chat over a bottle of whisky for two hours for a little more than £25, but those who return can expect to pay many times that, depending on their host, and food and drink.

Such extravagance is not unusual. A bottle of Dom Perignon "Gold", for example, costs 250,000 yen (roughly £1,800) while a vintage Romani-Conti will set you back 1.8m yen - Club Ai sells 20 a month.

Hard drinking is encouraged, because the hosts, aged from 20 to 68, depend on commissions. The more guests drink, the more reckless their spending.

The cavernous club, where 90 hosts can entertain up to 100 customers at a time, is a temple of kitsch. Huge chandeliers cast their light on dozens of gilded neo-classical statues below. Mirrors cover the walls and, of course, the ceiling.

Upstairs at street level hang pictures of the hosts, ranked according to their popularity. The flavour of this month - indeed the past few years - is Keisuke, a deeply tanned man with dyed wavy hair and a clear liking for baring his chest.

But the undisputed public face of Ai is Takeshi Aida, who opened the club in 1971 after making a name for himself as a persuasive door-to-door mattress salesman.

Now the owner of four lucrative clubs in Kabukicho, including one for lesbians, Mr Aida wears his wealth on his sleeve - a 25m yen diamond-encrusted watch.

He has little time for smaller host pubs around Tokyo that, together with more established clubs, are worth £335m a year.

"There is no comparison between here and those places," he says. "They don't follow safety standards or pay their taxes. We do. The police are welcome to drop by here any time they like."

Should they take him up on the offer they are unlikely to find anything more untoward than off-key karaoke crooners.

Yet a night at a host club isn't always innocent. There is the promise in seedier clubs - sometimes fulfilled - of sex.

Officially, it is not part of the service, but it is no secret that hosts end up in bed with customers, although many try not to.

"The danger is that if you sleep with customers, they won't come back to the club again, and that means losing a source of income," says one Tokyo host.

At Club Ai, Ryosuke, a 30-year-old with pencilled-in eyebrows, says he can separate his private and professional lives.

"I'm actually quite nervous when I talk to girls here," he says. "You have to be careful not to go too far in what you say and risk ruining the club's reputation by insulting someone. Of course, some of the women who come here are beautiful, and believe me I notice them. I don't act on my feelings, but I admit it's difficult to keep a lid on them sometimes."

Like his fellow hosts, Ryosuke was unwilling to reveal his earnings, but insiders say a good host can easily make £50,000 a month, rather more than most Japanese salarymen take home in a year.

But the glamorous side of hosting comes after a tough apprenticeship. Newcomers are expected to scrub toilets and take out the rubbish, and can only move on to full-time hosting once they prove they can attract high-spending punters.

There are risks, too, for the customers. Tales abound of young women lured into host clubs, run up huge bills and are forced to turn to prostitution to pay them.

As the clock ticks towards midnight on a weekday at Club Ai, the prospect of a hefty bill doesn't seem to trouble two young women in jeans and T-shirts who skip to their table, hosts in tow.

At the next table, an older woman laughs uproariously in between long slugs of strawberry margarita, her glass refilled regularly by one of seven hosts around her table. She is in for an expensive night.

Which is just as well, as some women are also exercising their right not to be impressed with this newfound freedom.

They include Reiko, a 23-year-old office worker on her first visit. "The hosts were quite intelligent, which surprised me, she said. "But they weren't nearly as good looking as I'd been expecting. I won't be going again."